Electric motor safe state control

ABSTRACT

The invention relates to the application domain of vehicle electric motor digital control and more specifically to the domain of functional safety mechanisms associated to that.

FIELD OF THE INVENTION

The invention relates to the application domain of vehicle electricmotor digital control and more specifically to the domain of functionalsafety mechanisms associated to that.

BACKGROUND OF THE INVENTION

FIG. 5 provides a typical digital controlled electric motor system.

-   -   1101: The digital control system    -   1102: The electric motor power stage (aka: Inverter)    -   1103: The electric motor (here is an example with 3 phases,        there may be more phases)    -   1104: The motor position sensor system    -   1105: The vehicle battery power line

The invention addresses a problem that occurs when a transient orpermanent fault leads to the situation where the digital control logicthat drives the electric motor power transistors is no more able toproperly operates.

In a vehicle, this digital controller is ASIL-D certified. This meansthat it contains the safety detection mechanism that can detect andreport the faulty situation mentioned above. In the best-case situation,the digital controller is able to automatically contain or repair thefault in an acceptable reaction time. In this case there is no need foradditional mechanism.

But in the worst-case situation, the digital controller is “dead”, andan emergency logic must be activated to handle the problem. This logicis able to override digital control signals to drive a safe state ofmotor power stages.

FIG. 6 provides a digital controlled eMotor system with safe statehandling.

-   -   1201: The Safe state management logic that overrides the power        stage control signals.

The basic safe state that can be applied in case of faulty digitalcontroller is the “Free wheel” mode. In this case all the power stageswitches are forced to open state. As a result, the motor coils are setin open circuit configuration, as shown in FIG. 7 .

As explained in FIG. 8 , an edge effect of the free wheel configurationis the induction of an electromagnetic voltage on motor coils pins.Depending on the motor speed, three situation are to be considered:

-   -   At low motor speed, this voltage is lower than the battery        voltage, therefore the protection diodes (1301) are blocked. No        current is injected backward to the battery. This situation is        safe.    -   Over a first speed threshold, the V_(EMF) voltage exceeds the        VBAT voltage. Then the protection diodes become passing. A        current is injected backward to the battery. The battery is able        to handle a certain amount of charge current. So the situation        is safe until the backward current is bellow battery maximum        rated charge current.    -   Over a second speed threshold, the backward injected current        exceeds the maximum supported by the battery. This situation is        dangerous and must be avoided.

FIG. 8 illustrates the free wheel problem at high speed that theinvention solves.

-   -   0401: First speed threshold where motor coil voltage exceeds        battery voltage.    -   0402: Second speed threshold where backward injected current        exceeds battery ratings.

As demonstrated above, the free wheel configuration is not a safe stateat high speed. In this situation another safe state can be used: theactive short circuit configuration. Is this configuration, the powerstage switches are controlled such as:

-   -   All switches on VBAT side are “open”    -   All switches on ground side are “closed”

FIG. 9 illustrates an eMotor system in “active short circuit” safe stateconfiguration.

-   -   1501: All motor coils are short circuited, so the        electromagnetic induction voltage is    -   null. Therefore there is no backward current injected to        battery.

Whereas this configuration is safe with regard to battery, it has somebad edge effects that must be taken into account:

-   -   The motor is strongly braking due to the short circuit current        flowing through the coils. Motor braking without vehicle driver        action may be dangerous. It may be acceptable at high speed, but        not at low speed.    -   Braking induces thermal energy dissipation in the system. This        is to be minimized as much as possible.

The above illustrates that the management of the eMotor safe state mustbe more intelligent than the ones provided so far.

IT IS THE AIM OF THE INVENTION

It is the aim of the invention to provide an intelligent management ofthe eMotor safe state which:

-   -   Select “active short circuit” safe state at high speed    -   Use “free wheel” whenever possible

SUMMARY OF THE INVENTION

The first aspect of the invention describes an (electric) motor basedsystem with enhanced safety, comprising: (1) an (electric) motor; (2) an(electric) motor power control means provided by controlling said(electric) motor; (3) a first (digital) control unit, adapted forproviding (generating) first control signals for said (electric) motorpower control means; (4) a (electric) power storage means, provided forpowering said (electric) motor power control means; (5) a first sensoradapted for determining information (110) related to the power exchangebetween said (electric) power storage means and said (electric) motorpower control means; (6) a second control unit, provided by enhancedsafety, wherein said second control unit is adapted for passing saidfirst control signals, received from said first (digital) control unit,to said (electric) motor power control means in a first mode and adaptedfor providing (generating) second control signals for said (electric)motor power control means in a second mode (instead of said firstcontrol signals) and wherein said second control unit inputs andexploits said information.

The second aspect of the invention described a second control unit,provided for enhanced safety, suitable for being part of an (electric)motor based system with enhanced safety, which comprises: (1) an(electric) motor; (2) an (electric) motor power control means providedby controlling said (electric) motor; (3) a first (digital) controlunit, adapted for providing (generating) first control signals for said(electric) motor power control means; (4) a (electric) power storagemeans, provided for powering said (electric) motor power control means;(5) a first sensor adapted for determining information related to thepower exchange between said (electric) power storage means and said(electric) motor power control means; the second control unit beingadapted for passing said first control signals, received from said first(digital) control unit, to said (electric) motor power control means ina first mode and adapted for providing (generating) second controlsignals for said (electric) motor power control means in a second mode(instead of said first control signals) and wherein said second controlunit inputs and exploits said information.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 describes an (electric) motor based system (10), comprising: (1)an (electric) motor (20); (2) an (electric) motor power control means(30); (3) a first (digital) control unit (40); (4) a (electric) powerstorage means (50); (5) a first sensor (60); and (6) a second controlunit (70).

FIG. 2 describes the (electric) motor based system (10) its modes ofoperation comprising: (a) a first mode (200), (b) a second mode (210),wherein in particular in said second mode (210) sub-modes such asfree-wheel mode (220) and active short circuit mode (230) are part.

FIG. 3 describes further embodiments of FIG. 1 , illustrating additionalsignals (140, 150) that the second control unit (70) may input, theoption of the first control unit (40) using also signal (110), theoption of having a motion sensor (80) and the use of the speedinformation (160) use by said first unit (40) and optionally even saidsecond unit (70).

FIG. 4 shows an embodiment of the second control unit (70) with one ormore elements it may comprise of such as a control logic unit (430)(which may include a timer), multiplexers (420) (note that a 2 controlsignal single multiplexer arrangement is also possible), a comparator(410), one or more storage means (90) and optionally ananalogue-to-digital convertor (400).

FIG. 5 shows the context of an prior-art (electric) motor based system,comprising: (1) an (electric) motor (1103); (2) an (electric) motorpower control means (1102); (3) a first (digital) control unit (1101);(4) the power lines (1105) originating from a (electric) power storagemeans (and a speed or motion sensor (1104));

FIG. 6 shows the context of an (electric) motor based system,comprising: (1) an (electric) motor (1103); (2) the power lines (1105)originating an (electric) motor power control means (1102); (3) a first(digital) control unit (1101); (4) a (electric) power storage means(1105) (and a speed or motion sensor (1104)), with the requirement ofhaving a safe state management unit (1201).

FIGS. 7 and 9 shows more detail on the an (electric) motor power controlmeans (1102) and in particular illustrate two different modes.

FIG. 8 shows the relationship between motor speed and the batterybackward injected current excess problem the invention solves.

FIG. 10 shows an embodiment of FIG. 6 , wherein the safe statemanagement unit (1201) exploits speed information (1601), which may bean unsatisfactory solution if this information becomes unavailable.

FIG. 11 shows an embodiment of FIG. 6 , wherein the safe statemanagement unit (1201) or second control unit (70) in accordance withthe invention exploits sensor information (1703), originating fromsensor (1702), placed in the between the power source or battery (1701)and the power lines.

FIG. 12 provides an embodiment of the flow chart of FIG. 2 .

FIGS. 13, 14 and 15 illustrate the operation caused by the inventedsecond control unit.

FIG. 16 illustrates the intrinsic safety of the proposed sequence.

DETAILED DESCRIPTION OF THE INVENTION

With reference to the prior art and the described problem to be solved,the most obvious possibility is to take benefit of the motor positionsensor that exist on the system. The idea is to inject this informationto the safe state manager that can deduce the motor speed based on thatand therefore take the appropriate decisions.

FIG. 10 illustrates such “state of art” solution to the problem.

-   -   1601: Motor speed sensor is re-used by the safe-state management        (0201)

The above solution suffers of several issues:

-   -   In the case where the motor control failure comes from a        position sensor defect, then the safe-state manager cannot work.        The solution would be to have a redundant motor position sensor.        This leads to important extra cost and mechanical constraints.    -   Using the position sensor for speed evaluation is a quite        complex operation. Therefore, the complexity of the safe-state        manager is quite high. This is obviously a problem in terms of        system cost. But also, it is a functional safety problem. The        more a system is complex, the higher the risk of failure is.    -   The relation between the motor speed and the resulting backward        current is not obvious. It depends on complex factors        (temperature, system aging, battery voltage). This means that        the safe-state manager must be even more complex to compute        those factors. Another solution is to take all the possible        margins at design time. This is not optimal and will not allow        to switch back to free wheel state at much as possible.

The invention uses another system architecture.

The invention relates to an (electric) motor based system (10) andrelated second control unit (70).

The invented system (10) and control unit (70) provide an enhancedsafety (electric) motor (20) system, in that, when faults occur in thenormal mode of operation (first mode (200)) (which may a variety ofreasons such as sensors or the primary (first (digital)) control unit(40) or combinations thereof fail), and when hence proper action isrequired to bring the entire system in to a safe mode, hence such actionto be provided with a additional (second (digital)) control unit (70)),one needs to ensure that such action does not cause additional problemssuch as a substantial power exchange from the (electric) motor back tosaid (electric) power storage means (50).

The invention describes an (electric) motor based system (10) withenhanced safety, comprising: (1) an (electric) motor (20); (2) an(electric) motor power control means (30) provided by controlling said(electric) motor (20); (3) a first (digital) control unit (40), adaptedfor providing (generating) first control (100) signals for said(electric) motor power control means (30); (4) a (electric) powerstorage means (50), provided for powering said (electric) motor powercontrol means (30); (5) a first sensor (60) adapted for determininginformation (110) related to the power exchange between said (electric)power storage means (50) and said (electric) motor power control means(30); (6) a second control unit (70), provided by enhanced safety,wherein said second control unit (70) is adapted for passing said firstcontrol signals (100), received from said first (digital) control unit(40), to said (electric) motor power control means (30) in a first mode(200) and adapted for providing (generating) second control signals(120) for said (electric) motor power control means (30) in a secondmode (210) (instead of said first control signals) and wherein saidsecond control unit (70) inputs and exploits said information (110).

In an embodiment of the invention the (electric) motor based system (10)described above is provided, wherein said second control unit (70)exploits said information (110) for providing (generating) secondcontrol signals for said (electric) motor power control means (30).

In an embodiment of the invention the (electric) motor based system (10)described is provided, wherein said second control unit (70) inputs afault signal (130) and exploits said fault signal (130) to switchbetween said modes.

Note the fault signal (130) may come from different sources and canoptionally be a plurality of fault signals (130) to be combined. In aparticular embodiment said fault signal (130) is provided by said first(digital) control unit (40).

The invention describes the (electric) motor based system (10), whereinsaid second control unit (70), upon receipt of said fault signal (130),provides (generates) second control signals (120) for preventingsubstantial power exchange from the (electric) motor to said (electric)power storage means (50), preferably second control signals (120) causea temporal brake effect on the (electric) motor when necessary (inparticular when said power exchange from the (electric) motor to said(electric) power storage means (50) is exceed a threshold).

More in particular a (electric) motor based system (10) may be provided,wherein said second control unit (70), upon receipt of said fault signal(130), provides (generates) second control signals (120) to put the(electric) motor in either free-wheel mode (220) (implying all switchesopen in said (electric) motor power control means (30)) or in activeshort circuit mode (230) (implying all switches to ground close and allswitching to power open in said (electric) motor power control means(30)), depending on monitoring said information (110), preferablyreassessing said information (110) after a predetermined time.

In a particular embodiment of the above in the (electric) motor basedsystem (10) said second control unit (70), upon receipt of said faultsignal (130), (a) provides (generates) second control signals (120) toput the (electric) motor in free-wheel mode (220) (implying all switchesopen in said (electric) motor power control means (30)); thereaftermonitoring said information (110) and upon exceeding a threshold (140),(b) said second control unit (70) provides (generates) second controlsignals (120) to put the (electric) motor in active short circuit mode(230) (implying all switches to ground close and all switching to poweropen in said (electric) motor power control means (30)); and thereafterafter a predetermined time (150) return to (a).

In an embodiment of the invention the (electric) motor based system (10)is provided, wherein said second control unit (70) is adapted forinputting said threshold (140). While this threshold may come fromseveral sources one of the possibilities is from said first (digital)control unit (40).

In an embodiment of the invention the (electric) motor based system (10)is provided, wherein said second control unit (70) is adapted forinputting said predetermined time (150). While this time may come fromseveral sources one of the possibilities is from said first (digital)control unit (40).

In the invention means to determine (especially unwanted) power exchangefrom the (electric) motor to said (electric) power storage means (50),like one or more sensors, even of different kind, are provided. It issufficient that such means or sensors capable of determining ordetecting a substantial power exchange, meaning one which may cause harmto the (electric) power storage means (50) are foreseen. These sensorscan be analogue, requiring extra digitalization means in the system forfurther digital use or in itself be digital. Examples are a currentsensor and a temperature sensor.

Note that typically in such (electric) motor based system (10) said(electric) motor power control means (30) comprises a plurality of pairwise serial connected switches (one pair per phase of the (electric)motor), more over most likely also each switch being provided withover-voltage protection (diodes).

Given its function to steer in normal mode the motor said first(digital) control unit (40) is typically a hardware programmable unit,preferably a programmable logic matrix.

Given its function to operate in essence in safe mode, the second(digital) control unit (70) may be a hardware block of various kind, buttypically it is of a lower complexity of said first (digital) controlunit (40), to avoid failure of itself as much as possible, henceprogrammability might be rather limited, for instance to inputting theparameters mentioned above.

It is to be appreciated that the introduction of extra hardware likesthe second control unit and the required sensors is an extra cost to beconsidered in the entire design. As this introduction is required forthe enhanced safety, trying to take most advantage of such presence isrecommended. Therefore in one embodiment of the invention, said firstcontrol unit (40) (if still operational or capable to do so, hence if itnot entirely fails) also exploits said information (110), for instanceto initiate further protection measures like cooling of said (electric)power storage means (50), change motor control algorithm, change motortorque regulation point and/or Communicate information to other systemsof the vehicle

It is worth mentioning that the described (electric) motor based system(10) typically comprising a (motion) sensor (80), suitable fordetermining speed information (160), wherein said first control unit(40) (also and/or in normal mode only (meaning not requires currentinformation) exploits said speed information (160). Note that failure ofthe speed sensor may precisely be the cause of going into safety mode.

Note however that the invention can also work for systems without motionsensors but use position estimates based on motor coil current.

Taking the same considerations into account based the presence of(additional) hardware and trying to make most advantage of suchpresence, one may opt to adapt said second control unit (70) to alsoexploits said speed information (160) (if still available), for instanceto verify whether the braking effect, it should cause in a certain modetemporally and under certain circumstances, is achieved. Thisintroduction of such option is subject to the requirement of keeping thecomplexity low.

The invention provides hence a second control unit (70), provided forenhanced safety, suitable for being part of an (electric) motor basedsystem (10) with enhanced safety, which comprises: (1) an (electric)motor (20); (2) an (electric) motor power control means (30) provided bycontrolling said (electric) motor (20); (3) a first (digital) controlunit (40), adapted for providing (generating) first control (100)signals for said (electric) motor power control means (30); (4) a(electric) power storage means (50), provided for powering said(electric) motor power control means (30); (5) a first sensor (60)adapted for determining information (110) related to the power exchangebetween said (electric) power storage means (50) and said (electric)motor power control means (30); the second control unit (70) beingadapted for passing said first control signals (100), received from saidfirst (digital) control unit (40), to said (electric) motor powercontrol means (30) in a first mode (200) and adapted for providing(generating) second control signals (120) for said (electric) motorpower control means (30) in a second mode (210) (instead of said firstcontrol signals) and wherein said second control unit (70) inputs andexploits said information (110).

In an embodiment of the invention, said second control unit (70),comprises storage means (90), to store said threshold (140) and/or saidpredetermined time (150).

In an embodiment of the invention said second control unit (70),comprises an analog-to-digital convertor (400) to digitize saidinformation (110) (and optionally even said speed information (160)).

In an embodiment of the invention said second control unit (70),comprises a comparator (410) to verify whether said information (110)exceeds said threshold.

In an embodiment of the invention said second control unit (70),comprises one or more selectors (multiplexers) (420) for selectingbetween (the control signals applicable for) said modes (200, 210, 220)based on said fault signal (130) and/or the outcome (170) of saidcomparator (410).

In an embodiment of the invention said second control unit (70),comprises a control logic unit (430), implementing a state machine, forchanging between said modes (200, 210, 220).

To ensure that the addition of the second control unit itself result insafe operation, the second control unit (70) is being designed with areaction time shorter than the dead-time of the motor control, hence alow complex hardware circuit is recommendable.

Finally, given the above mentioned considerations on cost and efficientuse of hardware and information, one may use a second control unit withmore elaborated features or even use of a more complex one in aparticular mode and revert to another simpler one (as the ones describedabove with the methods) in case the complex one fails. Suchconsideration always need to be balanced with a safety impact analysis(safety should be enhanced and not jeopardized) and the timing aspectindicated above must be respected also. A possible hierarchical approachis outlined in the following embodiment wherein the second control unit(70), exploits said information (110) (indirectly) by during normal(non-fault operation) inputting (motion) sensor (80) information,suitable for determining speed information (160), determining arelationship between said speed information (160) and said information(110) related to the power exchange between said (electric) powerstorage means (50) and said (electric) motor power control means (30);and upon receipt of said fault signal 130), exploit this relationship incombination with speed information (160) to derive computed information((180) for providing (generating) second control signals for said(electric) motor power control means (30) by (a) providing (generating)second control signals (120) to put the (electric) motor in free-wheelmode (220) (implying all switches open in said (electric) motor powercontrol means (30)); thereafter monitoring said computed information(180) and upon exceeding a threshold (140), (b) said second control unit(70) provides (generates) second control signals (120) to put the(electric) motor in active short circuit mode (230) (implying allswitches to ground close and all switching to power open in said(electric) motor power control means (30)); and thereafter after apredetermined time (150) return to (a), optionally in case said motionsensor is no longer available, apply the 3 mode procedure describedearlier.

The invention uses a system architecture as shown in FIG. 11 .

-   -   1701: The vehicle battery    -   1702: A current sensor is added on battery power line to measure        battery current (IBAT)    -   1703: The measured battery current is used by the safe state        manager (1201)

FIG. 12 explains the behavior of the safe state manager:

-   -   1801: This is the normal operation state. In this state, the        safe-state manager does not have any influence on the system.    -   1802: Whenever a fault is reported by the logic controller fault        manager, then the state-state manager is activated    -   1803: The first action is to immediately set the system in        “free-wheel” safe mode.    -   1804: Then the safe-state manager continuously monitors the        current level reported by the VBAT current sensor.        -   If the backward injected current is bellow battery maximum            rating, then the system is maintained in free-wheel state        -   Else, the system is switched to short-circuit safe state    -   1805: In short circuit safe state the motor braking. The battery        current is no more relevant because of the VBAT power switches        set to “open” state. So, in this situation, the safe-state        manager has no clue for deciding to switch back to free-wheel        state.    -   1806: The short-circuit state is maintained for an arbitrary        amount of time, then a tentative switch back to free-wheel is        done. At this stage, the above sequence is played again.

FIGS. 13, 14, 15 are showing the resulting system behavior is differentmotor speed conditions:

In the situation of FIG. 13 , the fault occurs when the motor is at lowspeed, then the safe-state manager keeps the system in free-wheelbecause backward current never exceeds battery ratings

In the situation of FIG. 14 , the fault occurs when the motor is at highspeed. The safe-state manager starts with free-wheel but detects highbackward current. Then is immediately switches to short-circuit for anarbitrary amount of time. The it tries again the free-wheel. Thissequence happens several times until the backward current in free-wheelis under battery ratings.

In the situation of FIG. 15 , the fault occurs when the motor is at highspeed. The sequence starts like previous example. But for some reason,the vehicle accelerates again in free-wheel (descending road). Theproposed solution is able to react to this situation dynamically.

While a safety issue may be opposed to the proposed solution:

-   -   Obviously, the solution allows the backward current to exceed        the battery rating during a short period corresponding to the        time required for the safe-state manager to detect the over        current and switch to short-circuit state.

To demonstrate that this issue has no consequence on system safety weneed to consider the dead-time topic.

The dead-time is a normal operation action that must be used each timethe power switch controls are inverted. In this situation, because ofthe propagation delay uncertainty, there may be a transient shortcircuit in the system. This is highly damageable! To avoid thissituation, a short period of “all open” state if inserted. FIG. 16explains this.

As you can see, the intermediate dead-time configuration is exactly thesame as the “free-wheel” safe state situation.

And, we can assume that the of the safe-state manager reaction time isof the same order of duration as the above normal operation dead-time.

So, the transient over-current of free-wheel in the invention is no moredangerous than the normal motor control.

1. A (electric) motor based system (10), comprising: (1) an (electric)motor (20); (2) an (electric) motor power control means (30) provided bycontrolling said (electric) motor (20); (3) a first (digital) controlunit (40), adapted for providing first control (100) signals for said(electric) motor power control means (30); (4) a (electric) powerstorage means (50), provided for powering said (electric) motor powercontrol means (30); (5) a first sensor (60) adapted for determininginformation (110) related to the power exchange between said (electric)power storage means (50) and said (electric) motor power control means(30); (6) a second control unit (70), wherein said second control unit(70) is adapted for passing said first control signals (100), receivedfrom said first (digital) control unit (40), to said (electric) motorpower control means (30) in a first mode (200) and adapted for providingsecond control signals (120) for said (electric) motor power controlmeans (30) in a second mode (210) and wherein said second control unit(70) inputs and exploits said information (110).
 2. The (electric) motorbased system (10) of claim 1, wherein said second control unit (70)exploits said information (110) for providing second control signals forsaid (electric) motor power control means (30).
 3. The (electric) motorbased system (10) of claim 1 or 2, wherein said second control unit (70)inputs a fault signal (130) and exploits said fault signal (130) toswitch between said modes.
 4. The (electric) motor based system (10) ofclaim 3 or 4, wherein said second control unit (70), upon receipt ofsaid fault signal (130), provides second control signals (120) forpreventing substantial power exchange from the (electric) motor to said(electric) power storage means (50), preferably second control signals(120) cause a temporal brake effect on the (electric) motor whennecessary.
 5. The (electric) motor based system (10) of claim 3 or 4,wherein said second control unit (70), upon receipt of said fault signal(130), provides second control signals (120) to put the (electric) motorin either free-wheel mode (220) or in active short circuit mode (230,depending on monitoring said information (110), preferably reassessingsaid information (110) after a predetermined time.
 6. The (electric)motor based system (10) of claim 3, 4 or 5, wherein said second controlunit (70), upon receipt of said fault signal (130), (a) provides secondcontrol signals (120) to put the (electric) motor in free-wheel mode(220; thereafter monitoring said information (110) and upon exceeding athreshold (140), (b) said second control unit (70) provides secondcontrol signals (120) to put the (electric) motor in active shortcircuit mode (230); and thereafter after a predetermined time (150)return to (a).
 7. The (electric) motor based system (10) of claim 6,wherein said second control unit (70) being adapted for inputting saidthreshold (140).
 8. The (electric) motor based system (10) of claim 6 or7, wherein said second control unit (70) being adapted for inputtingsaid predetermined time (150
 9. The (electric) motor based system (10)of any of the previous claims 1 to 8, wherein said first sensor (60)being a current sensor.
 10. The (electric) motor based system (10) ofany of the previous claims 1 to 8, wherein said first sensor (60) beinga temperature sensor.
 11. The (electric) motor based system (10) of anyof the previous claims, wherein said (electric) motor power controlmeans (30) comprises a plurality of pair wise serial connected switches.12. The (electric) motor based system (10) of any of the previousclaims, wherein said first (digital) control unit (40) being a hardwareprogrammable unit, preferably a programmable logic matrix.
 13. The(electric) motor based system (10) of any of the previous claims,further comprising a (motion) sensor (80), suitable for determiningspeed information (160), wherein said first control unit (40) exploitssaid speed information (160.
 14. The (electric) motor based system (10)of claim 6, wherein said second control unit (70), comprises storagemeans (90), to store said threshold (140) and/or said predetermined time(150).
 15. The (electric) motor based system (10) of claim 6, whereinsaid second control unit (70), comprises an analog-to-digital convertor(400) to digitize said information (110).
 16. The (electric) motor basedsystem (10) of claim 6, wherein said second control unit (70), comprisesone or more selectors (420) for selecting between said modes (200, 210,220) based on said fault signal (130) and/or the outcome (170) of acomparator (410).
 17. The (electric) motor based system (10) of claim 6,wherein said second control unit (70), comprises a control logic unit(430), implementing a state machine, for changing between said modes(200, 210, 220).
 18. A second control unit (70), suitable for being partof an (electric) motor based system (10), which comprises: (1) an(electric) motor (20); (2) an (electric) motor power control means (30)provided by controlling said (electric) motor (20); (3) a first(digital) control unit (40), adapted for providing first control (100)signals for said (electric) motor power control means (30); (4) a(electric) power storage means (50), provided for powering said(electric) motor power control means (30); (5) a first sensor (60)adapted for determining information (110) related to the power exchangebetween said (electric) power storage means (50) and said (electric)motor power control means (30); the second control unit (70) beingadapted for passing said first control signals (100), received from saidfirst (digital) control unit (40), to said (electric) motor powercontrol means (30) in a first mode (200) and adapted for providingsecond control signals (120) for said (electric) motor power controlmeans (30) in a second mode (210) and wherein said second control unit(70) inputs and exploits said information (110).
 19. The second controlunit (70) of claim 18, adapted for exploiting said information (110) forproviding second control signals for said (electric) motor power controlmeans (30).
 20. The second control unit (70) of claim 18 or 19, adaptedfor inputting a fault signal (130) and exploiting said fault signal(130) to switch between said modes.
 21. The second control unit (70) ofclaim 20, wherein said second control unit (70), upon receipt of saidfault signal (130), provides second control signals (120) for preventingsubstantial power exchange from the (electric) motor to said (electric)power storage means (50), preferably second control signals (120) causea temporal brake effect on the (electric) motor when necessary.
 22. Thesecond control unit (70) of claim 20, wherein said second control unit(70), upon receipt of said fault signal (130), provides second controlsignals (120) to put the (electric) motor in either free-wheel mode(220) or in active short circuit mode (230, depending on monitoring saidinformation (110), preferably reassessing said information (110) after apredetermined time.
 23. The second control unit (70) of claim 20,wherein said second control unit (70), upon receipt of said fault signal(130), (a) provides second control signals (120) to put the (electric)motor in free-wheel mode (220; thereafter monitoring said information(110) and upon exceeding a threshold (140), (b) said second control unit(70) provides second control signals (120) to put the (electric) motorin active short circuit mode (230); and thereafter after a predeterminedtime (150) return to (a).
 24. The second control unit (70) of claim 23,being adapted for inputting said threshold (140).
 25. The second controlunit (70) of claim 22 or 23, being adapted for inputting saidpredetermined time (150).
 26. The second control unit (70) of claim 23,comprising storage means (90), to store said threshold (140) and/or saidpredetermined time (150).
 27. The second control unit (70) of claim 23,comprising an analog-to-digital convertor (400) to digitize saidinformation (110).
 28. The second control unit (70) of claim 23,comprising one or more selectors (420) for selecting between said modes(200, 210, 220) based on said fault signal (130) and/or the outcome(170) of a comparator (410).
 29. The second control unit (70) of claim23, comprising a control logic unit (430), implementing a state machine,for changing between said modes (200, 210, 220).
 30. The second controlunit (70) of claim 23, being designed with a reaction time shorter thanthe dead-time of the motor control.